Structure

ABSTRACT

A structure of the present invention is the structure which is formed of a base made of a metal and an inorganic material surface layer made of crystalline and amorphous inorganic materials, wherein thermal conductivity of the inorganic material surface layer is lower than the thermal conductivity of the base, infrared emissivity of the inorganic material surface layer is higher than the infrared emissivity of the base, and the base is an annular body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority based on Japanese patentapplication JP 2006-247063 filed on Sep. 12, 2006. The contents of thisapplication are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a structure.

2. Discussion of the Background

It is desired that, in heating furnaces used for growing crystals andthe like at a high temperature, a time for raising the temperature to apredetermined processing temperature be short in order to shorten theprocessing time, while it is also desired that the temperature in thefurnace should not rise excessively over the processing temperatureafter the temperature has reached the predetermined processingtemperature, in order to make the heat treatment temperature stable.

For example, when growing an InGaSb crystal, a lump of GaSb material isplaced in a heating furnace and an InGaSb material is placed thereon,and the heating furnace is inductively heated so that the temperature inthe heating furnace is held between the melting point of GaSb (712° C.)and the melting point of InGaSb (in the range of 525° C. to 712° C.).When heating is carried out in this manner, only the InGaSb materialmelts to form an InGaSb crystal solution, which accumulates on top ofthe GaSb lump. Therefore, an InGaSb monocrystal can be grown by bringinga GaSb seed crystal into contact with this solution and pulling it upwhile rotating it, maintaining constant temperature of the InGaSbsolution.

In the above mentioned process, it is desirable that the time forraising the temperature in the heating furnace to 525° C. or higher beshort, while the temperature of the furnace should not exceed 712° C.

On this condition, in order to shorten the time for raising thetemperature, it is effective to improve the heat insulating propertyinside the furnace in a low temperature region, thus, it is consideredto be desirable to fabricate the furnace body (inner wall of thefurnace) from a material having excellent heat insulating property,namely, a material having a low thermal conductivity.

Further, in order to prevent excessive rising of the temperature in thefurnace exceeding the processing temperature, it is effective to enhancethe heat releasing property in a high temperature region so that thetemperature of the furnace body cannot easily rise in a high temperatureregion. Therefore, it is considered to be desirable to fabricate afurnace body from a material having excellent heat releasing property,namely, a material having a high emissivity.

Here, JP-A 2-47555 discloses a far infrared radiator comprises aninorganic compound coating film formed of oxide based ceramics andhigh-expansion glass with a low melting point on the surface of a metalbase, as a material having excellent heat releasing property.

Further, JP-A 3-62798 discloses an infrared radiator comprises ahigh-infrared radiation coating film (black color at room temperature)formed of metal oxide and high-expansion glass with a low melting pointon the surface of a metal base, as a material having similarly excellentheat releasing property.

The contents of JP-A 2-47555, JP-A 3-62798 are incorporated herein byreference in their entirety.

SUMMARY OF THE INVENTION

The structure of the present invention is a structure formed of a basemade of a metal and an inorganic material surface layer made ofcrystalline inorganic material and amorphous inorganic material, whereinthermal conductivity of the above mentioned inorganic material surfacelayer is lower than the thermal conductivity of the above mentionedbase, infrared emissivity of the above mentioned inorganic materialsurface layer is higher than the infrared emissivity of the abovementioned base, and the above mentioned base is an annular body.

Further, it is desirable that, in the structure of the presentinvention, the thermal conductivity of the above mentioned inorganicmaterial surface layer at room temperature be at least about 0.1 W/mKand at most about 2.0 W/mK.

Further, it is desirable that, in the structure of the presentinvention, the emissivity of the above mentioned inorganic materialsurface layer at room temperature at a wavelength in the range of 1 μmto 15 μm be at least about 0.70 and at most about 0.98.

Further, it is desirable that, in the structure of the presentinvention, a degree of irregularities (Rz_(JIS)) on the surface of theabove mentioned base be about 1/60 or more of a thickness of the abovementioned inorganic material surface layer.

Further, it is desirable that, in the structure of the presentinvention, the inorganic material surface layer be formed on the outersurface of the base, on the inner surface of the base, or on both of theouter surface and the inner surface of the base.

Further, it is desirable that, in the structure of the presentinvention, the material of the base includes steel, iron, copper,Inconel, Hastelloy, Invar, or stainless steel; the crystalline inorganicmaterial be at least one kind selected from the group consisting ofmanganese dioxide, manganese oxide, iron oxide, cobalt oxide, copperoxide and chromium oxide; and the amorphous inorganic material be atleast one kind selected from the group consisting of barium glass, boronglass, strontium glass, alumina-silicate glass, soda zinc glass and sodabarium glass.

Further, it is desirable that, in the structure of the presentinvention, the softening temperature of the amorphous inorganic materialbe at least about 400° C. and at most about 1000° C.; and the differencein the thermal expansion coefficient between the inorganic materialsurface layer and the base be about 10×10⁻⁶/° C. or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view schematically showing the manner in which radiationand reflection occur inside the structure of the present invention.

FIGS. 2A, 2B, 2C and 2D are perspective views schematically showingrespective examples of the structure of the present invention.

FIG. 3 is a perspective view, with a portion missing, schematicallyshowing an evaluation apparatus for evaluating performance of thestructure of the present invention.

DESCRIPTION OF THE EMBODIMENTS

First, the structure of the present invention is described withreference to the drawings.

The structure of the present invention is a structure formed of a basemade of a metal (hereinafter also referred to as metal base) and aninorganic material surface layer made of crystalline and amorphousinorganic materials, wherein thermal conductivity of the above mentionedinorganic material surface layer is lower than the thermal conductivityof the above mentioned base, infrared emissivity of the above mentionedinorganic material surface layer is higher than the infrared emissivityof the above mentioned base, and the above mentioned base is an annularbody.

FIGS. 2A, 2B, 2C and 2D are perspective views schematically showingexemplary structures of the present invention. FIGS. 2A and 2B showstructures in cylindrical shapes and FIGS. 2C and 2D show structures incylindroid shapes, and an inorganic material surface layer is formed onthe outer surface or the inner surface of each base.

Since these all have the same properties, a description of the structureof the present invention will be set forth in the structure incylindrical shape shown in FIG. 2A as an example.

A structure 10 shown in FIG. 2A has a double structure where the outersurface of a metal base 11 in cylindrical shape made of a metal iscoated with an inorganic material surface layer 12 made of crystallineand amorphous inorganic materials so that two kinds of materials havingdifferent radii adhered with each other.

Further, the inorganic material surface layer 12 is formed so that thethermal conductivity at room temperature is lower than that of the metalbase 11 and the infrared emissivity at room temperature is higher thanthat of the metal base 11.

Here, in the present description, “room temperature” refers to atemperature at about 25° C.

Further, in the present description, thermal conductivity of theinorganic material surface layer is the thermal conductivity of amixture of a crystalline inorganic material and an amorphous inorganicmaterial at room temperature, and is determined by the respectivethermal conductivities of the crystalline inorganic material and theamorphous inorganic material which form the inorganic material surfacelayer, the ratio of mixture and the like.

Further, the inorganic material surface layer 12 which forms thestructure of the present invention is formed so that its thermalconductivity is lower than the thermal conductivity of the metal base 11throughout the entirety of a low temperature region.

Further, though the low temperature region and the high temperatureregion in the present description differ depending on the applicationand a material of the metal base and inorganic material surface layerwhich form the structure, and are not particularly limited, for example,in the case where the metal base is made of an SUS430 material and theinorganic material surface layer is formed of a crystalline inorganicmaterial comprising MnO₂ and CuO and an amorphous inorganic materialcomprising SiO₂—BaO glass, the low temperature region is at least about0° C. and at most about 500° C., and the high temperature region is atleast about more than 500° C. and at most about 1000° C.

Since, in the structure of the present invention, the thermalconductivity of the inorganic material surface layer is lower than thatof the metal base, for example, in the structure 10 of the presentinvention having a shape as shown in FIG. 2A, when the metal base 11 isheated by a heater which is attached to the inside of the metal base 11or when the metal base 11 is heated with a heat source which is providedin the space inside the metal base 11, the rate of thermal conduction tothe metal base 11 and the space inside the metal base 11 is high, whilethe rate of thermal conduction from the metal base 11 to the outside ofthe structure 10 through the inorganic material surface layer 12 is low.Therefore, the structure 10 of the present invention is a materialhaving high heat insulating property as a whole and does not easilyrelease heat to the outside in a low temperature region.

Accordingly, the temperature of the metal base 11 and in the spaceinside the metal base 11 can be quickly raised when heating the insidethe structure 10 of the present invention.

Further, the infrared emissivity of the inorganic material surface layer12 is higher than the infrared emissivity of the metal base 11. In thepresent description, the infrared emissivity of the inorganic materialsurface layer is the infrared emissivity of a mixture of a crystallineinorganic material and an amorphous inorganic material at roomtemperature, and is a property which is represented by the average valueof the emissivity throughout the entirety of the infrared region.

Further, the inorganic material surface layer 12 which forms thestructure of the present invention is formed so that its infraredemissivity is higher than the infrared emissivity of the metal base 11in a high temperature region as well.

Here, the rate of radiative transfer from an object per unit area isproportional to the product of the temperature of the object to the 4thpower and the emissivity of the object according to theStefan-Boltzmann's law. Therefore, since the effects of the term of thetemperature of the object to the 4th power become great in the hightemperature region, the rate of radiative transfer dramaticallyincreases in comparison with that in the low temperature region.

Therefore, since the rate of radiative transfer to radiate heat to theoutside of the structure 10 through the inorganic material surface layer12 can be increased by increasing the infrared emissivity of theinorganic material surface layer 12, the structure 10 of the presentinvention becomes a material having excellent heat releasing property,and thus, easily releases heat to the outside.

Accordingly, by using the structure 10 of the present invention, therise of the temperature of the metal base 11 and in the space inside themetal base 11 in the high temperature region can be prevented.

Further, since the structure of the present invention is an annularbody, leaking of a gas or a liquid from the inside of the structure tothe external space can be prevented. Therefore, the heat insulatingproperty inside the structure can be secured.

Further, by making the structure of the present invention an annularbody, the temperature inside the structure can be decreased by improvingthe heat releasing property in the high temperature region where theheat releasing property depends on radiation.

Here, “the annular body” in the present description refers to, in athree-dimensional Cartesian coordinates where X, Y and Z axes areperpendicular to each other, a form closed in at least one plane amongX-Y, Y-Z and Z-X planes. Accordingly, the annular body in the presentdescription includes those of which the cross section perpendicular tothe longitudinal direction is not only circular, but elliptical andrectangular.

Though the reason why the heat releasing property improve by making thestructure of the present invention an annular body is not clear, asshown in FIG. 1, when radiant heat 2 from heat source 1 enters into theinner wall of structure 10, radiant heat 3 is radiated from the surfaceof the structure 10 and the reflected radiant heat 4 enters into theinner wall of the structure 10 again. Then, radiant heat 5 is radiatedagain from the surface of the structure 10, and the reflected radiantheat 6 again enters into the inner wall of the structure 10. In thismanner, it is assumed that the radiant heat is reflected continuously sothat heat release progresses in the case where the structure is anannular body, and therefore, the heat releasing property is improved.

Further, though the above mentioned heat source is not particularlylimited, examples include a furnace body, a heater, a reactive gas andoil for heating.

In particular, by making the structure of the present invention anannular body, a high temperature gas or liquid, such as a reactive gasor oil for heating as the above mentioned heat source, can run throughinside the structure without being leaked to the external space.

As the material of the above mentioned base, metals such as steel, ironand copper, nickel-based alloys such as Inconel, Hastelloy and Invar,and other alloys such as stainless steel and the like, can be used.Since these metal materials have high thermal conductivity, in the casewhere these are used as the material of the base of the structure of thepresent invention, the rate of thermal conduction to the base and thespace inside the base can be increased. Therefore, the time for raisingthe temperature to a predetermined temperature can be shortened.

Further, since these metal materials have high heat resistance, themetal materials can be used optimally in a temperature of at least about500° C. and at most about 1000° C. Further, by using these metalmaterials for the base, the structure of the present invention becomesthe relatively low cost structure superior in thermal shock resistance,processability and physical property.

A desirable lower limit of the thickness of the above mentioned base isabout 0.2 mm, more desirably about 0.4 mm and a desirable upper limit isabout 10 mm, more desirably about 4 mm.

This is because, in the case where the thickness is within theabove-mentioned range, the structure tends to have sufficient strength,and the time for raising the temperature of the base tends to becomeshort.

The above mentioned inorganic material surface layer is formed ofcrystalline and amorphous inorganic materials. Though the crystallineinorganic material is not particularly limited, it is desirable to usean oxide of a transition metal, and at least one kind selected from thegroup consisting of manganese dioxide, manganese oxide, iron oxide,cobalt oxide, copper oxide and chromium oxide is desirable.

The thermal conductivity of an oxide of transition metals like these islow in comparison with that of the metal base, and therefore, the rateof thermal conduction to the outside of the structure through theinorganic material surface layer can be decreased, and thus, thestructure of the present invention becomes a structure having excellentheat insulating property.

Further, since an oxide of transition metals like these has a highemissivity in the infrared region, an inorganic material surface layerhaving a high emissivity can be formed. Therefore, the structure of thepresent invention becomes a structure having excellent heat releasingproperty.

The inorganic material surface layer may be provided on the outersurface of the annular-shaped metal base 11 and 31 as shown in FIGS. 2Aand 2C, or may be provided on the inner surface of the annular-shapedmetal base 21 and 41 as shown in FIGS. 2B and 2D.

Further, the inorganic material surface layer may be provided on boththe inner and outer surface of the annular-shaped base. In this case,the heat insulating property and heat releasing property can be furtherimproved.

The amorphous inorganic material is not particularly limited, however,it is desirable to use at least one kind selected from the groupconsisting of barium glass, boron glass, strontium glass,alumina-silicate glass, soda zinc glass and soda barium glass.

Since these amorphous inorganic materials are low melting glass of whichthe softening temperature is at least about 400° C. and at most about1000° C., an inorganic material surface layer can be formed on thesurface of a metal base easily and firmly by melting and applying thematerial onto the surface of a metal base, followed by a heating andfiring process.

Further, since the thermal conductivity of these amorphous inorganicmaterials is low in comparison with that of the metal base, the rate ofthermal conduction to the outside through the inorganic material surfacelayer can be decreased, and thus, the structure of the present inventionbecomes a structure having excellent heat insulating property.

Here, the thermal expansion coefficient of the crystalline inorganicmaterial made of an oxide of a transition metal, among the materialsthat form the inorganic material surface layer, is as low as at leastabout 8×10⁻⁶/° C. and at most about 9×10⁻⁵/° C., while the thermalexpansion coefficient of the amorphous inorganic material made of lowmelting glass is as high as at least about 8×10⁻⁶/° C. and at most about25×10⁻⁶/° C., and therefore, it is possible to control the thermalexpansion coefficient of the inorganic material surface layer byadjusting the mixture ratio of the above mentioned crystalline inorganicmaterial and the above mentioned amorphous inorganic material. Forexample, since the thermal expansion coefficient of stainless steel,that is the metal base, is at least about 10×10⁻⁶/° C. and at most about18×10⁻⁶/° C., by adjusting the mixture ratio of the above mentionedcrystalline inorganic material and the above mentioned amorphousinorganic material, the thermal expansion coefficient of the inorganicmaterial surface layer and that of the metal base can be made close, andthus, adhesiveness between the inorganic material surface layer and themetal base can be increased.

The desirable thermal expansion coefficient for the inorganic materialsurface layer differs, depending on the combination with the metalmaterial of the base, but it is desirable that the difference in thethermal expansion coefficient between the inorganic material surfacelayer and the metal base be about 10×10⁻⁶/° C. or less.

Though the mixture ratio of the crystalline inorganic material in theinorganic material surface layer can be adjusted in order to control theheat expansion coefficient as described above, a desirable lower limitis about 10% by weight, more desirably about 30% by weight, while adesirable upper limit is about 90% by weight, more desirably about 70%by weight. In the case where the mixture ratio of the crystallineinorganic material is within the above range, the heat releasingproperty at high temperatures tends to be excellent, and also theadhesiveness with the metal base tends to be excellent.

Further, a desirable lower limit of the thickness of the inorganicmaterial surface layer is about 2 μm, and a desirable upper limit isabout 50 μm. In the case where the thickness is within the above range,the heat insulating property at low temperatures tends to be excellent,and also formation of a film on the base (formation of inorganicmaterial surface layer) tends to become easier.

Further, though the form of the structure of the present invention isnot particularly limited, as long as it is an annular body, cylindricalform and cylindroid form, as shown in FIGS. 2A, 2B, 2C and 2D aredesirable.

In the case of cylindrical form, as shown in FIG. 2A, a desirable lowerlimit of the diameter (outer diameter) is about 5 mm and a desirableupper limit is about 200 mm. By setting the diameter in the abovementioned range, heat releasing property and heat insulating propertycan be effectively gained.

Further, in the structure of the present invention, it is desirable thatthe thermal conductivity of the above mentioned inorganic materialsurface layer at room temperature be at least about 0.1 W/mK and at mostabout 2.0 W/mK.

The thermal conductivity of the inorganic material surface layer at roomtemperature can be measured using any of known measuring methods, forexample, hot wire method, laser flash method and the like.

However, when the structure of the present invention is measured as itis, the thermal conductivity of the entire structure including the metalbase is measured, and as the thermal conductivity of the inorganicmaterial surface layer cannot be measured, it is necessary to separatelyprepare a sample for measurement.

More specifically, a crystalline inorganic material and an amorphousinorganic material are crushed and mixed at a predetermined ratio. Next,the mixture is heated to a temperature of the melting point of theamorphous inorganic material or more and kneaded in a state where theamorphous inorganic material is molten, and then, cooled and solidifiedto form a solid.

By processing this solid into a form which is appropriate for therespective measuring methods, and thus, the thermal conductivity can bemeasured using any of known measuring method.

The thermal conductivity of the oxide of a transition metal which can beused as the crystalline inorganic material is at least about 0.5 W/mKand at most about 2.0 W/mK at room temperature, while the thermalconductivity of low melting glass which can be used as an amorphousinorganic material is at least about 0.1 W/mK and at most about 1.2 W/mKat room temperature. Therefore, in the case where an inorganic materialsurface layer is prepared using these crystalline inorganic material andamorphous inorganic material, the thermal conductivity can be adjustedto at least about 0.1 W/mK and at most about 2.0 W/mK at roomtemperature.

In the structure of the present invention, when the thermal conductivityof the inorganic material surface layer at room temperature is at leastabout 0.1 W/mK and at most about 2.0 W/mK, the rate of thermalconduction to the outside through the inorganic material surface layercan be made considerably low. Therefore, a structure having highlyexcellent heat insulating property in a low temperature region can beprovided.

Further, in the structure of the present invention, it is desirable thatthe emissivity of the above described inorganic material surface layerfor a wavelength in the range of 1 μm to 15 μm be at least about 0.70and at most about 0.98 at room temperature.

The emissivity of the inorganic material surface layer may be measuredon the surface of the structure of the present invention on which theinorganic material surface layer is formed, or measured using a samplefor measurement which is separately prepared in the same manner as forthe measurement of the thermal conductivity. As for the method formeasurement, a known spectrophotometry method can be used.

The emissivity of the oxide of a transition metal which can be used asthe crystalline inorganic material for a wavelength in the range of 1 μmto 15 μm at room temperature is at least about 0.75 and at most about0.98, while the emissivity of low melting glass which can be used as theamorphous inorganic material for a wavelength in the range of 1 μm to 15μm at room temperature is at least about 0.65 and at most about 0.96.Therefore, in the case where an inorganic material surface layer isprepared using these crystalline inorganic material and amorphousinorganic material, the emissivity can be kept at least about 0.70 andat most about 0.98.

The wavelength range of 1 μm to 15 μm is a so-called near infrared andfar infrared region and has great thermal effects. In the case where theemissivity in this region is at least about 0.70 and at most about 0.98,particularly in a high temperature region, the rate of radiativetransfer from the inorganic material surface layer to the outside can bemade considerably high. Accordingly, a structure having highly excellentheat releasing property in the high temperature region can be provided.

In addition, it is desirable that, in the structure of the presentinvention, the degree of irregularities (Rz_(JIS)) on the surface of theabove mentioned base be about 1/60 or more of the thickness of the abovementioned inorganic material surface layer. Here, Rz_(JIS) is aten-point mean Roughness, defined in accordance with JIS B 0601: 2001.

The contents of JIS B 0601:2001 are incorporated herein by reference intheir entirety.

When irregularities is formed on the surface of the base, the inorganicmaterial surface layer can be made to adhere more firmly to the base, incomparison with a case where the surface of the base is smooth, and itis possible to form an inorganic material surface layer which does notpeel even after the repetitive rises and falls of the temperature.

Further, in the case where the degree of irregularities on the surfaceof the base is about 1/60 or more of the thickness of the inorganicmaterial surface layer, the inorganic material surface layer is formedalong the irregularities on the surface of the base. Therefore thesurface area of the inorganic material surface layer becomes larger, incomparison with a case where the surface of the base is smooth and thearea which contributes to radiative transfer become wider, and thereby,the heat releasing property of the structure of the present inventioncan further be improved.

Next, a method for manufacturing a structure of the present invention isdescribed.

The method for manufacturing a structure of the present inventionincludes the following steps of: a surface processing step of a metalbase, a mixing step for preparing slurry by wet blending a crystallineinorganic material and an amorphous inorganic material, a coating stepfor applying the slurry to the metal base, and a firing step in whichfiring the metal base to which the slurry has been applied to fix aninorganic material coating film to the metal base.

First, the surface processing step to process the surface of a metalbase is carried out.

The Surface processing of a metal base is a step in which impurities onthe metal base is removed and irregularities is formed on the surface ofthe metal base, if necessary.

A method for removing impurities on a metal base is not particularlylimited, and a general washing method can be used. For example, a methodof ultrasonic cleaning in an alcohol solvent, and the like, can be used.

A method for forming irregularities on the surface of a metal base isalso not particularly limited, a sandblasting, an etching or a hightemperature oxidizing can be included as exemplary methods. Thesemethods may be used alone, or a plurality of methods may be used incombination. As the above mentioned method for forming irregularities,any method that has been used conventionally can be adopted.

Here, the step of forming irregularities on the surface of a metal baseis not an essential step, and may be omitted depending on the case.

Next, the mixing step of wet blending a crystalline inorganic materialand an amorphous inorganic material is carried out.

In this step, a powdery crystalline inorganic material and a powderyamorphous inorganic material are respectively prepared so as to have apredetermined particle size and form, the respective powders are dryblended at a predetermined mixture ratio to prepare mixed powder, andfurthermore, a slurry is prepared by adding water thereto and wetblending the mixture in a ball mill.

Though the mixture ratio of the mixed powder and water is notparticularly limited, approximately 100 parts by weight of water to 100parts by weight of mixed powder is desirable. This is because it isnecessary to provide the slurry with an appropriate viscosity in orderto apply to a metal base. Further, an organic solvent may be used, ifneeded.

Subsequently, the coating step of applying the slurry to the metal baseis carried out.

In this step, the slurry that has been prepared in the mixing step isapplied to the metal base, the surface of which has been processed inthe surface processing step. The applying method is not particularlylimited as long as it is a method that the slurry can be uniformlyapplied to the metal base, and spray coating, transferring or brushcoating may be included as exemplary methods.

Subsequently, the firing step of firing the metal base, to which theslurry has been applied, is carried out.

In this step, after drying the metal base to which the slurry has beenapplied in the coating step, heating and firing are carried out to forman inorganic material surface layer. It is desirable that the firingtemperature be the melting point of the amorphous inorganic material ormore, and the temperature at least about 700° C. and at most about 1100°C. is desirable, though it depends on the type of the mixed amorphousinorganic material. By setting the firing temperature to be the meltingpoint of the amorphous inorganic material or more, the metal base andthe amorphous inorganic material can adhere firmly to each other andthus, an inorganic material surface layer which does not peel even afterthe repetitive rises and falls of the temperature can be formed.

EXAMPLES

Herein below, examples of the present invention will be set forth,describing in greater detail of the present invention. However, thepresent invention is not to be limited to only these examples.

Example 1 Manufacture of Metal Base

A cylinder made of an SUS430 material of which the thermal conductivityat room temperature (hereinafter referred to as λ) was 25 W/mK and thethermal expansion coefficient measured in a range from room temperatureto 500° C. (hereinafter referred to as a) was 10.4×10⁻⁶/° C., having athickness of 2 mm and a diameter of 100 mm was cut into a piece of alength of 100 mm, which was used as a metal base.

Further, two discs for lids made of the same material as the abovementioned cylinder, having a thickness of 2 mm and a diameter of 100 mmwere prepared.

Subsequently, the parts were assembled into a pillar-shaped form.

More specifically, by welding the two discs for lids to the both openingends of the metal base as a bottom face and an upper face, the openingswere sealed and thus, a pillar-shaped body was formed.

Next, a surface processing step of washing and roughening the outersurface of the pillar-shaped body was carried out, in which ultrasonicwashing in an alcohol solvent and a sandblasting was carried out on thepillar-shaped body.

The sandblasting was carried out for 10 minutes using SiC abrasive grain#600.

Here, the Rz_(JIS) on the surface of the metal base was measured afterthe surface processing step, and it was 1.5 μm.

(Formation of Inorganic Material Surface Layer)

Next, 65% by weight of MnO₂ powder and 5% by weight of CuO powder ascrystalline inorganic materials, 30% by weight of BaO—SiO₂ glass powderas an amorphous inorganic material were dry mixed to prepare mixedpowder, and 100 parts by weight of water was added to 100 parts byweight of the mixed powder, and wet blended in a ball mill, thereby aslurry was prepared.

Further, the crystalline inorganic material and the amorphous inorganicmaterial in this composition were crushed and mixed, and then, heated toa temperature of the melting point of the amorphous inorganic materialor more and kneaded in a state where the amorphous inorganic materialwas molten, and cooled and solidified to form a solid, and λ wasmeasured using a quick thermal conductivity meter (QTM-500, made byKyoto Electronics Manufacturing Co., Ltd.). Further, a was measured in arange from room temperature to 500° C. using a TMA (thermo mechanicalanalysis) apparatus (TMA8310, made by Rigaku Corporation). The resultsare shown in Table 1.

The coating step, in which this slurry was applied onto the outersurface of the above mentioned pillar-shaped body by spray coating, wascarried out.

Subsequently, after drying the above mentioned pillar-shaped body, onwhich a coating layer was formed by spray coating, for two hours at 100°C., the firing step of heating and firing the pillar-shaped body for onehour at 700° C. in the air was carried out to form an inorganic materialsurface layer 102, and thereby, a pillar-shaped structure 100 wasmanufactured (see FIG. 3).

The emissivity of the formed inorganic material surface layer 102 for awavelength in the range of 1 μm to 15 μm at room temperature wasmeasured using a spectrophotometer (measuring apparatus: system 200model, made by Perkin Elmer, Inc.). Further, the thickness of the formedinorganic material surface layer 102 was measured. The results are shownin Table 2.

(Formation of Through Hole)

A through hole having a length of 52 mm×a width of 52 mm was formed inthe center portion on the bottom of the pillar-shaped structure 100manufactured through the above mentioned process, in order to provide aceramic heater which will be described later.

(Fabrication of Evaluation Apparatus)

FIG. 3 is a perspective view with a portion missing schematicallyshowing an evaluation apparatus for evaluating the performance of thestructure of the present invention. In the present view, the uppersurface and the front side face are omitted.

In this evaluation apparatus 160, a ceramic heater 161 having a lengthof 50 mm×a width of 50 mm×a height of 20 mm is placed in the centerportion of the pillar-shaped structure 100, and the temperature in thespace inside the structure can be raised through heating using theheater.

Further, a thermocouple 162 is placed in a location at a distance of 10mm from the inner bottom face of the structure 100, so that thetemperature in the space inside the structure can be measured.

The ceramic heater 161 and the thermocouple 162 were installed and wiredthrough the through hole provided at the bottom of the structure 100,and further, the ceramic heater 161 was supported at the bottom, whichwas joined to a supporting pillar 163.

Further, the structure 100 was mounted on a mounting pillar 164 made ofthe same material as the metal base 101, so that the major part of thebottom face of the structure 100 did not make a direct contact withother portions.

The performance of the structure was evaluated using the evaluationapparatus 160.

(Evaluation of Heat Insulating Property in Low Temperature Region)

2 kW of electric power was supplied to the ceramic heater 161 and thetime for the temperature indicated by the installed thermocouple 162rising to 500° C. was measured. The results are shown in Table 2.

(Evaluation of Heat Releasing Property in High Temperature Region)

The temperature indicated by the thermocouple 162 was measured as themaximum temperature, at the point in time when the amount of releasedheat and the supplied electric power reached a point of balance and thetemperature became constant, in a state where 2 kW of electric power wasbeing supplied to the ceramic heater 161. The results are shown in Table2.

(Evaluation of Adhesiveness of Inorganic Material Surface Layer)

A process of supplying electric power to the ceramic heater 161 to raisethe temperature in the space inside the structure to 800° C. and coolingthe space to room temperature through natural heat release wasconsidered as one cycle, and a test was carried out by repeating theprocess for ten cycles. After carrying out the test, whether or not theinorganic material surface layer 102 had peeled off the metal base 101was visually observed. The results are shown in Table 2.

Examples 2 and 3

The ratio of the amorphous inorganic material, the type of crystallinematerial and the base material were respectively provided as shown inTable 1, and these were used to manufacture structures in the samemanner as in Example 1.

Here, the ratio of the crystalline material was the ratio gained bysubtracting the ratio of the amorphous inorganic material shown in Table1 from 100%, and in the case where the crystalline material was made oftwo types of materials, the composition was respectively, MnO₂: CuO=65%by weight: 5% by weight and MnO₂: Fe₃O₄=65% by weight: 5% by weight.

In each Example and the like, λ and α of the metal base and theinorganic material surface layer, and the emissivity of the inorganicmaterial surface layer were measured in the same manner as in Example 1.The results are shown in Table 1.

Further, in each Example and Reference Example, the surface processingstep was carried out so that the Rz_(JIS) on the surface of the baseafter surface processing became the value shown in Table 2, by changingthe processing time for a sandblasting on the metal material.

Further, in each Example and Reference Example, the coating step wascarried out so that the thickness of the inorganic material surfacelayer shown in Table 2 was provided, by changing the conditions forspray coating the slurry.

In each Example and Reference Example, the performance of the structurewas evaluated using the evaluation apparatus 160, in each of themanufactured structures in the same manner as in Example 1.

The results of evaluation are collectively shown in Table 2.

Examples 4, 7, and Reference Examples 1, 2

The ratio of the amorphous inorganic material, the type of crystallinematerial and the base material are respectively provided as shown inTable 1, and these are used to manufacture structures in the same manneras in Example 1.

Here, the ratio of the crystalline material is the ratio gained bysubtracting the ratio of the amorphous inorganic material shown in Table1 from 100%, and in the case where the crystalline material is made oftwo types of materials, the composition is respectively, MnO₂: Cuo=65%by weight: 5% by weight and MnO₂: Fe₃O₄=65% by weight: 5% by weight.

In each Example and the like, λ and α of the metal base and theinorganic material surface layer, and the emissivity of the inorganicmaterial surface layer are measured in the same manner as in Example 1.The results supposed to be obtained are shown in Table 1.

Further, in each Example and Reference Example, the surface processingstep is carried out so that the RZ_(JIS) on the surface of the baseafter surface processing becomes the value shown in Table 2, by changingthe processing time for a sandblasting on the metal material.

Further, in each Example and Reference Example, the coating step iscarried out so that the thickness of the inorganic material surfacelayer shown in Table 2 is provided, by changing the conditions for spraycoating the slurry.

In each Example and Reference Example, the performance of the structureis evaluated using the evaluation apparatus 160, in each of thestructures to be manufactured in the same manner as in Example 1.

The results of evaluation supposed to be obtained are collectively shownin Table 2.

Example 5

Before the parts are assembled into a pillar-shaped form, the surfaceprocessing step, in which the inner surface of the metal base is washedand roughened, is carried out by executing ultrasonic washing of themetal base with cylindrical form in an alcohol solvent and then aprocess of sandblasting, in the same manner as in Example 1.

Further, the same surface processing step is carried out on either oneface of the two discs for lids.

A slurry is prepared in the same manner as in Example 1, and the coatingstep of applying this slurry on the inner surface of the metal base incylindrical form and either one face of the discs for lids (surface onwhich sandblasting process is carried out) by spray coating is carriedout.

After that, the firing step is carried out, in the same manner as inExample 1, and thus, an inorganic material surface layer is formed.

The two discs for lids are welded to the bottom face and the upper faceof the metal base and placed in such a manner that the surface on whichthe inorganic material surface layer is formed at the inner surface ofthe structure, and thereby the openings are sealed to manufacture apillar-shaped structure.

After that, the performance of the structure is evaluated using theevaluation apparatus 160, in the same manner as in Example 1.

The conditions and the results of evaluation supposed to be obtained arecollectively shown in Tables 1 and 2.

Example 6

First, a pillar-shaped structure, on the inner surface of which aninorganic material surface layer is formed, is manufactured in the samemanner as in Example 5.

Next, a surface processing and the formation of an inorganic materialsurface layer on the outer surface are carried out on the pillar-shapedstructure in the same manner as in Example 1, and thus, a structurehaving an inorganic material surface layer both on the outer surface andthe inner surface is manufactured.

After that, the performance of the structure is evaluated using anevaluation apparatus 160, in the same manner as in Example 1.

The conditions and the results of evaluation supposed to be obtained arecollectively shown in Tables 1 and 2.

Reference Example 3

A structure having an inorganic material surface layer is manufacturedin the same manner as in Example 1, except that 65% by weight of quartzpowder as a crystalline inorganic material, 30% by weight of BaO—SiO₂glass powder and 5% by weight of fly ash as amorphous inorganicmaterials are dry blended to prepare mixed powder. After that, theperformance of the structure is evaluated using an evaluation apparatus160, in the same manner as in Example 1.

The conditions and the results of evaluation supposed to be obtained arecollectively shown in Tables 1 and 2.

Comparative Example 1

A structure as manufactured in the same manner as in Example 1, exceptthat no inorganic material surface layer was formed on the metal baseand the discs for lids. After that, the performance of the structure wasevaluated using an evaluation apparatus 160, in the same manner as inExample 1. Further, the measurement of the emissivity was carried out inthe surface of the metal base, in the same manner as in Example 1.

The conditions and the results of evaluation are collectively shown inTables 1 and 2.

Comparative Example 2

A metal base in cylindrical form which is the same as that used inExample 1 is cut at two places parallel to the longitudinal direction,so that a metal base in cylindrical form missing the ¼ of the side faceis manufactured.

After that, the above mentioned metal base in cylindrical form and discsfor lids are assembled, so that a pillar-shaped body having an openingportion on the side face is manufactured, and the rest of the process iscarried out in the same manner as in Example 1, and thus, a structurehaving an inorganic material surface layer on the outer surface ismanufactured.

After that, the performance of the structure is evaluated using anevaluation apparatus 160, in the same manner as in Example 1.

The conditions and the results of evaluation supposed to be obtained arecollectively shown in Tables 1 and 2. Here, the structure to bemanufactured in Comparative Example 2 has a form of which the side isnot closed, and therefore, is a structure of which the base does nothave the form of an annular body. TABLE 1 thermal expansion thermalconductivity coefficient α ratio of amorphous (W/mK) ({acute over ( )}10⁻⁶/° C.) inorganic material crystalline base inorganic materialinorganic material (wt %) material material base surface layer basesurface layer Example 1 30 MnO_(2,) CuO SUS430 25 1.2 10.4 8.3 Example 230 MnO₂, Fe₃O₄ SUS430 25 1.3 10.4 7.8 Example 3 70 MnO_(2,) CuO SUS30418 1.2 17.2 9.5 Example 4 10 MnO₂, Fe₃O₄ SUS430 25 1.3 10.4 7.5 Example5 30 MnO_(2,) CuO SUS430 25 1.2 10.4 8.3 Example 6 30 MnO_(2,) CuOSUS430 25 1.2 10.4 8.3 Example 7 30 mullite SUS304 18 1.2 17.2 6.3Reference Example 1 90 MnO_(2,) CuO SUS304 18 1.2 17.2 10.1 ReferenceExample 2 30 Al₂O₃ SUS430 25 2.8 10.4 8.5 Reference Example 3 35 quartzpowder SUS430 25 0.8 10.4 5.4 Comparative Example 1 — — SUS430 25 — 10.4— Comparative Example 2 30 MnO_(2,) CuO SUS430 25 1.2 10.4 8.3

TABLE 2 thickness of degree of time for raising inorganic materialirregularities temperature maximum annular coated surface layer A onsurface of base (seconds) temperature Presence of body (*) emissivitysurface (μm) (Rz_(JIS): μm) B/A (RT→ 500° C.) (° C.) peel-off Example 1◯ 0.96 outer surface 20 1.5 0.075 162 763 Not present Example 2 ◯ 0.94outer surface 30 0.5 0.017 155 785 Not present Exanple 3 ◯ 0.96 outersurface 5 1.5 0.300 172 739 Not present Example 4 ◯ 0.98 outer surface25 1.2 0.048 177 658 Not present Example 5 ◯ 0.96 outer surface 20 1.50.075 158 792 Not present Example 6 ◯ 0.96 outer surface + 20 1.5 0.075140 365 Not present inner surface Example 7 ◯ 0.94 outer surface 5 1.50.300 183 755 Present Reference ◯ 0.92 outer surface 30 0.2 0.007 188710 Present Example 1 Reference ◯ 0.96 outer surface 25 1.2 0.048 205644 Not present Example 2 Reference ◯ 0.42 outer surface 20 1.3 0.065145 932 Not present Example 3 Comparative ◯ 0.30 — — 1.5 — 250 980 —Example 1 Comparative X 0.96 outer surface 20 1.5 0.075 275 583 Notpresent Example 2(*) ◯: the form of base is annular bodyX: the form of base is not annular body

As is clear from Tables 1 and 2, the time for raising the temperature isshort and the maximum temperature is low in the structures manufacturedin Examples 1 to 7.

In the structure manufactured in Comparative Example 1, the time forraising the temperature is long and the maximum temperature is high. Thereason for this is considered that the thermal conductivity is high andthe heat insulating property at low temperatures is poor, and further,the emissivity is low and the heat releasing property at hightemperatures is poor due to the absence of inorganic material surfacelayer.

The time for raising the temperature is presumed to be long and themaximum temperature is presumed to be low in the structure manufacturedin Comparative Example 2. The reason for this is considered that thebase does not have the form of an annular body, and therefore, the hightemperature gas leaks to the external space through the opening, makingthe heat insulating property poor.

Further, the time for raising the temperature is very short and themaximum temperature is extremely low, and there is no peeling of theinorganic material surface layer in any of the structures manufacturedin Examples 1 to 6.

From the above results, a structure formed of a base made of a metal andan inorganic material surface layer made of crystalline and amorphousorganic materials, the thermal conductivity of the above mentionedinorganic material surface layer at low temperatures is lower than thethermal conductivity of the above mentioned base, the infraredemissivity of the above mentioned inorganic material surface layer ishigher than the infrared emissivity of the above mentioned base, and theabove mentioned base is an annular body, has excellent heat insulatingproperty in a low temperature region and excellent heat releasingproperty in a high temperature region.

In particular, it can be seen that when the thermal conductivity of theabove mentioned inorganic material surface layer at room temperature isin the range of 0.1 W/mK to 2 W/mK, the heat insulating property can beimproved a great deal, when the emissivity of the above mentionedinorganic material surface layer for a wavelength in the range of 1 μmto 15 μm at room temperature is in the range of 0.7 to 0.98, the heatreleasing property can be improved a great deal, and when the degree ofirregularities (Rz_(JIS)) on the surface of the base is 1/60 or more ofthe thickness of the above described inorganic material surface layer,the above described inorganic material surface layer can be made toadhere firmly to the base.

In the structure of the present invention, the base made of a metalmaterial is an annular body surrounding a heat source (heater, furnacebody or fluid), and as an inorganic material surface layer havingthermal conductivity lower than thermal conductivity of the base andinfrared emissivity higher than that of the base is formed on thesurface (inner surface or outer surface) of the base, heat release fromthe inside of the structure is blocked to secure heat insulatingproperty in a low temperature region, where the heat releasingproperties depends on the thermal conduction, and heat release isaccelerated to decrease the temperature inside the structure in a hightemperature region, where the heat releasing property depends onradiation.

1. A structure which is formed of a base made of a metal and aninorganic material surface layer made of crystalline inorganic materialand amorphous inorganic material, wherein thermal conductivity of saidinorganic material surface layer is lower than the thermal conductivityof said base, infrared emissivity of said inorganic material surfacelayer is higher than the infrared emissivity of said base, and said baseis an annular body.
 2. The structure according to claim 1, wherein thethermal conductivity of said inorganic material surface layer at roomtemperature is at least about 0.1 W/mK and at most about 2.0 W/mK. 3.The structure according to claim 1, wherein the emissivity of saidinorganic material surface layer at room temperature at a wavelength inthe range of 1 μm to 15 μm is at least about 0.70 and at most about0.98.
 4. The structure according to claim 1, wherein a degree ofirregularities (Rz_(JIS)) on the surface of said base is about 1/60 ormore of the thickness of said inorganic material surface layer.
 5. Thestructure according to claim 1, wherein said inorganic material surfacelayer is formed on the outer surface of said base, on the inner surfaceof said base, or on both of the outer surface and the inner surface ofsaid base.
 6. The structure according to claim 1, wherein the materialof said base includes steel, iron, copper, Inconel, Hastelloy, Invar, orstainless steel.
 7. The structure according to claim 1, wherein saidcrystalline inorganic material comprises at least one kind selected fromthe group consisting of manganese dioxide, manganese oxide, iron oxide,cobalt oxide, copper oxide and chromium oxide.
 8. The structureaccording to claim 1, wherein said amorphous inorganic materialcomprises at least one kind selected from the group consisting of bariumglass, boron glass, strontium glass, alumina-silicate glass, soda zincglass and soda barium glass.
 9. The structure according to claim 1,wherein the softening temperature of said amorphous inorganic materialis at least about 400° C. and at most about 1000° C.
 10. The structureaccording to claim 1, wherein the difference in the thermal expansioncoefficient between said inorganic material surface layer and said baseis about 10×10⁻⁶/° C. or less.